shims

I was working on designing a piston o ring bullet today and they have a really small base. 4.3mm. I was using a 10mm brim at .1mm thick. Looking at the brim after taking it off the bullet I thought it looked a lot like the shims that were in the regulator. Thickness seemed awful close...

Examples: shims on the piston spring (not shown) increase X as the shims get thicker shims under the HP seat (or a thicker seat) decrease X shims between the HP seat carrier (not shown) and the regulator body increase X. Do I have this right?